They should have no effect on how the car reacts to a head on collision. Nor should it have anyrhing to do with the crumple zones.

 

the xbrace is mounted to the engine subframe...so unless the engine is being crumpled I don't think the xbrace will make any difference in a collision.

 

I've included some information in the library here: https://www.s2ki.com/article/archive/9/

And it includes pictures and a brief description of the "STB"s that we have. But note - we don't have struts in our cars, we have shocks, so its a shock tower brace. Therefore it doesn't yield as much of an improvement as it would on a strut suspension. But that's because the strut suspension needs all the help it can get.